Rheology-Processing/Ch.1 1

ΕΙΣΑΓΩΣΗ ΣΤΗ ΡΕΟΛΟΓΙΑΚΑΙ ΚΑΤΕΡΓΑΣΙΑ ΠΟΛΥΜΕΡΩΝ

ΠΑΝΕΠΙΣΤΗΜΙΟ ΘΕΣΣΑΛΙΑΣ – ΠΟΛΥΤΕΧΝΙΚΗ ΣΧΟΛΗΤΜΗΜΑ ΜΗΧΑΝΟΛΟΓΩΝ ΜΗΧΑΝΙΚΩΝ

ΜΜ820 (ΕΝ2500)ΠΡΟΠΤΥΧΙΑΚΟ ΜΑΘΗΜΑ 2017-2018

Διδάσκων: Δρ. Νικόλας ΠολυχρονόπουλοςEmail: npolychron@mie.uth.gr

Rheology-Processing/Ch.1 2

INTRODUCTION TO POLYMERRHEOLOGY AND PROCESSING

UNIVERSITY OF THESSALY – SCHOOL OF ENGINEERINGDEPARTMENT OF MECHANICAL ENGINEERING

ΜΜ820 (ΕΝ2500)UNDERGRADUATE COURSE 2017-2018

Instructor: Dr. Nickolas D. PolychronopoulosEmail: npolychron@mie.uth.gr

Rheology-Processing/Ch.1 3

Αντικείμενο μαθήματος: Τα πολυμερή είναι υλικά πολλαπλών χρήσεων τα

οποία παρουσιάζουν σημαντικές διακυμάνσεις στη ρεολογική τους

συμπεριφορά καθώς και στις ιδιότητες κατά την κατεργασία τους. Ο σκοπός

του παρόντος μαθημάτος είναι να εισάγει τους φοιτητές (α) στις έννοιες

ρεολογίας των πολυμερών και στον μηχανολογικό εξοπλισμό που

χρησιμοποιείται στη σχετική βιομηχανία και (β) να εξηγήσει την

αλληλοσύνδεση μεταξύ μοριακής δομής πολυμερών, διαδικασίας

κατεργασίας και ιδοτήτων του τελικού μορφοποιημένου προϊόντος.

Rheology-Processing/Ch.1 4

Βαθμολόγηση: Ο κάτωθι πίνακας παρουσιάζει τα ΠΟΣΟΣΤΑ βάσει των οποίων

υπολογίζεται ο ΤΕΛΙΚΟΣ ΒΑΘΜΟΣ

Παράδειγμα: Έστω φοιτητής βαθμολογείται με 7/10 στις εβδομαδιαίες εργασίες, και

6/10 στη τελική εξέταση. ΤΕΛΙΚΟΣ ΒΑΘΜΟΣ=(7×0.5)+(6×0.5)= 6.5/10

Η κάθε εβδομαδιαία εργασία θα παραδίδεται την τελευταία μέρα (Παρασκευή) της

επόμενης εβδομάδας. Όταν μια εβδομαδιαία εργασία δεν παραδίδεται εγκαίρως,

αυτομάτως αυτή η εργασία παίρνει βαθμό 0/10.

Εβδομαδιαία εργασία 50 %

Τελική εξέταση 50 %

Rheology-Processing/Ch.1 5

CHAPTER 1

Fundamentals of Polymer Science

Rheology-Processing/Ch.1 6

POLYMER comes from Greek and means “many parts”. Polymers i.e. plastics andrubber are substances whose molecules form long chains.

repeating unit (part)

Polymers are characterized through the physical and chemical natureof the repeating units in the chains.

The world PLASTICS usually implies materials• Having low strength and stiffness• Having temperature limitations• Deforming continuously under applied force

Rheology-Processing/Ch.1 7

• By 1980’s, volumetric consumption of plastics hasexceeded steel annually

• Why ??• Easily shaped or molded into complex shapes with minimum

fabrication and finishing• Low densities i.e. low-weight products or parts• Thermal and electrical insulators• Other special properties e.g. flexible, transparent, chemical

resistance, etc…

Rheology-Processing/Ch.1 8

Rheology-Processing/Ch.1 9

MAJOR COMMERCIAL PLASTICS

High Density Polyethylene (HDPE)containers, bottles, wire and cableinsulation and household appliances.

Low Density Polyethylene (LDPE)bottles, film, garment bags, wirecoating and toys.

Linear Low Density Polyethylene (LLDPE)thin high-strength film.

Polyvinyl Chloride (PVC)RIGID PVC: pipe and housing applications.PLASTICIZED PVC: flexible film sheet, upholstery

Rheology-Processing/Ch.1 10

Polypropylene (PP)automotive parts, appliances, fibers, luggage, etc..

Polystyrene (PS)sporting goods, radio and TV housings,automotive parts etc..

Nylon (polyamides)food and health packages,endovascular devices (balloon catheters)

Polyethylene Terephthalate (PET)film, bottles, fibers etc.

Polycarbonate (PC)compact disks (CD), optical fibers

Rheology-Processing/Ch.1 11

Other polymers:

• Polymethyl Methacrylate (PMMA)

• Acrylonitrile-Butadiene-Styrene (ABS)

• Polytetrafluoroethylene (PTFE)

• Polyetheretheroketone (PEEK)

• Polyethersulfone (PES)

Rheology-Processing/Ch.1 12

New types of fiber-reinforcedcomposites exhibit highperformance and long servicelife.

Extensively used inaircraft/aerospace applicationsnot only for military aircraft butalso in commercial aviation

They replace metal parts,providing more strengthand lower weight, in theworld's largest passengerjet AIRBUS A380(600+passengers),

Lyon PPS 32, 2016, AIRBUS

Rheology-Processing/Ch.1 13

Blades must be:- very large- very light- and very strong

Therefore:COMPOSITES

glass fiber?, carbon fiber? graphene?environmental, cost considerations?

Another example: Wind turbines

Rheology-Processing/Ch.1 14

PLASTIC PIPES CYPRUS-TURKEY https://www.youtube.com/watch?v=ixacYA-fjOY

80 KM Long, 1600 mm diameter, POLYETHYLENE pipe for FRESH WATER FROM TURKEY TO CYPRUS

Rheology-Processing/Ch.1 15

• A few, but expensive, parts for aircraft/aerospace applications.

• Now, greater emphasis is being put on automotive, electrical,housing and packaging applications.

We must produce many parts at high production speeds andlow costs, but with high performance and long service lifecharacteristics.

Rheology-Processing/Ch.1 16

PRODUCTION STEPS

MONOMER e.g. ETHYLENE (gas) ~ 0.80 EURO/kg (2017)

polymerize it

POLYMER e.g. POLY-ETHYLENE (solid) ~ 1.4 EURO/kg (2017)

melt it and shape it

PROCESS e.g. EXTRUDE to produce film, pipe, etc…. (processingcost ~ 2 × 1.4 = 2.8 EURO/kg)

Roughly, the raw materials cost accounts for about 50% of the final product, but, of course, itwill depend on the performance requirements.

Rheology-Processing/Ch.1 17

POLYMER PRODUCERSIn Greece: ECO Thessaloniki (PVC), Northern Greece PP plant, more ??? DOW in Lavrio???

SABIC, BASF, BAYER, EXXONMOBIL, SHELL, DOW-DUPONT, BP, TOTAL, etc….perhaps 50 big chemicalcompanies in the world.

PROCESSORSIn Greece: PLASTIKA KRITIS (films for greenhouses), HELLENIC CABLES (large diameter cables) and lots of

other small manufacturers

In the whole world: roughly 100,000 companies (10~10,000 people)

MACHINE MANUFACTURERSIn Greece: NONE

In the world: Reifenhäuser, Huskey Injection Molding, Krauss-Maffei, Erema, Milacron, Battenfeld-Cincinnati etc….

Global total business of plastics: 1 TRILLION US DOLLARS per year. Volume of plastics produced per year is about 325 MILLION tons (2017)

Rheology-Processing/Ch.1 18

PLASTICS GET A LOT OF BAD PRESS BECAUSE OF POLLUTIONIN OCEANS ETC…

SOLUTIONS:1. RECYCLING (most difficult problem is collection) PLASTIC isPERHAPS THE ONLY MATERIAL THAT IS 100% RECYCLABLE(recycling requires efforts by individuals and governments).

2. BIODEGRADABLE POLYMERS (yes they exist, they areproduced, but more expensive)

Rheology-Processing/Ch.1 19

Rheology-Processing/Ch.1 20

A FEW HISTORICAL REMARKS

• Polymers have been around since life began in this planet (leather,wood, wool, cotton and DNA are polymeric substances)

• Synthetic polymers were an important part of the industrialrevolution

o In 1839 the U.S. inventor Charles Goodyearinvented the process of vulcanization (heattreatment of a rubber and sulfur compound)which lead to products of considerabledurability.

Rheology-Processing/Ch.1 21

A FEW HISTORICAL REMARKS

Spoke first time in a conferencein 1917 for the above. But facedconsiderable opposition.

Colloid

single polymer chain (simulation)

Hermann Staudinger

A major step toward the Age ofPlastics was a German scientist,Hermann Staudinger (1953 NobelPrize, Chemistry) who realized thatpolymers were not colloids butrather long chains of repeatingunits (macromolecules)

Rheology-Processing/Ch.1 22

POLYMER STRUCTURE

In the simplest case, a polymer consists of a simple repeating unit:

The most important type of linear polymers are vinyl polymers:

If R → H POLYETHYLENE (PE)

R → CH3 POLYPROPYLENE (PP)

R → Phenyl POLYSTYRENE (PS)

R → Cl POLYVINYL CHLORIDE (PVC)

CHCH 2

R

|

Rheology-Processing/Ch.1 23

Polymer chains may be:

LINEARBRANCHED(the branches may beeither short or long andmay themselves havebranches)

CROSS-LINKED(to form a 3D Network Structure, e.g.like vulcanized rubber. They are unableto flow and are hard solids)

Rheology-Processing/Ch.1 24

POLYMER TYPES

• Thermoplastics: Melted by heating. Solidified by cooling. Can be re-melted (PS, PE, PVC, etc..)

• Thermosets: Long-chain molecules in fluid state. Harden usually byapplication of heat and pressure, due to cross-linking. They cannot besoftened again to make them flow (e.g. phenol formaldehyde, epoxies,most polyurethanes, etc..). Typical product Bakelite black phones.

• Elastomers: Cross-linked network structures with large deformabilityand complete recoverability due to high degree of chain flexibility (e.g.natural rubber) → RUBBERS

Rheology-Processing/Ch.1 25

Thermoplastics and thermosets are usually called plastics.

They are compounded, i.e. combined with other materials to give acompound in the form of pellets, granules, powder, flakes or liquid.

Combinations involve: AdditivesFillers or ReinforcementsOther polymers

Rheology-Processing/Ch.1 26

Commercial Classification of Thermoplastics

COMMODITYLDPE, HDPE, PP, PS, PVC Low performance

INTERMEDIATEPMMA, ABS

ENGINEERINGPC, NYLON 66 + 30% glass, PPS

ADVANCEDLiquid Crystal Polymer (LCP), PTFE, PEEK, PES Very high performance

Rheology-Processing/Ch.1 27

GLASS TRANSITION AND MELTING POINT

Polymers exist in crystalline (ordered)

or amorphous (random) states.

For amorphous polymers there is a certain temperature called theGLASS TRANSITION TEMPERATURE, Tg, below which the materialbehaves like glass, i.e. it is hard and rigid.

Crystalline polymers also exhibit Tg, but this is masked to some extendby the crystalline structure. It corresponds to low mobility in thebackbone of the chain.

Rheology-Processing/Ch.1 28

We consider Tg as the lowest temperature at which we canconsider the material “FLOWABLE LIKE A LIQUID”.

The melting point Tm is more meaningful for semi-crystalline polymers.

Rheology-Processing/Ch.1 29

Polymer TgoC Tm

oC Usual melt processing

range oC

Melt density kg/m3

HDPE -100 135 160-240 780

LDPE -100 110 160-240 760

PP -15 165 180-240 720

PVC (rigid) 80 240 170-200 1270

PS 100 - 180-240 1000

Rubber -70 35 90-110

PET 70 265 275-290 1210

Nylon-66 40 265 275-290 980

Nylon-6 40 220 230-260 980

NOTE: solid density is roughly 15% -20% HIGHER THAN MELT DENSITY

Rheology-Processing/Ch.1 30

MOLECULAR WEIGHT AND MOLECULAR WEIGHT DISTRIBUTION

Molecular Weight (MW) of WATER H₂O: 2×1+16=18

Ethylene monomer -(C₂H₄)- molecular weight (MW): 12×2+4×1=28

POLYETHYLENE (many monomer units)

-x-x-(C₂H₄)-(C₂H₄)-(C₂H₄)-(C₂H₄)-(C₂H₄)-x-x-

(C₂H₄)₅₀ WAX (MW: 50×28=1400)

(C₂H₄)₅₀₀₀ FILM RESIN (MW: 5000×28=140000)

Rheology-Processing/Ch.1 31

Commercial polymers generally contain a distribution ofmolecular weights. This distribution is specified in terms ofaverage molecular weights:

Number – Average: Mn

Weight – Average: Mw

Z – Average: Mz

Z+1 – Average: Mz+1

Rheology-Processing/Ch.1 32

A typical Molecular Weight Distribution (MWD) curve

Molecular Weight

Nu

mb

er

of

Mo

lecu

les

Rheology-Processing/Ch.1 33

If the number of molecules with molecular weight Mi is given by ni, thetotal weight of the sample is ΣniMi and the total number of molecules is Σni

Definition

This is the number-average molecular weight. If the weight fraction ofmaterial having a molecular weight Mi is wi, we have

weighttotal

Mofweight

W

Mn

Mn

Mnw iii

ii

iii

iii WwMn

i

ii

M

wWn Thus:

i

ii

nn

MnM

Also:

Rheology-Processing/Ch.1 34

Definition of Mn:

Definition of weight-average molecular weight:

the z-average molecular weight:

and the z+1-average molecular weight:

i

i

i

i

ii

n

M

w

w

n

MnM

i

ii

ii

ii

ww

Mw

Mn

MnM

2

ii

ii

ii

ii

zMw

Mw

Mn

MnM

2

2

3

2

3

3

4

1

ii

ii

ii

ii

zMw

Mw

Mn

MnM

Rheology-Processing/Ch.1 35

Example: Consider a polymer for which 99% of the weight is material with M=20,000 and1% with M=109. Determine Mn, Mw, Mz and Mz+1.

202,20

10

01.0

000,20

99.0

1

9

i

i

i

n

M

w

wM

79

101

1001.0000,2099.0

i

ii

ww

MwM

9

7

1822

1010

1001.0000,2099.0

ii

ii

zMw

MwM

9

182

273

2

3

1 101001.0000,2099.0

1001.0000,2099.0

ii

ii

zMw

MwM

Rheology-Processing/Ch.1 36

The ratio Mw/Mn is often called “POLYDISPERSITY”. For mostcommercial polymers, Mw ~ 10,000 – 400,000. The polydispersityvaries according to the polymerization method, etc.

Commercial PS: Mw/Mn ~ 2.5-4Commercial PP: Mw/Mn ~ 5-10Commercial PE: Mw/Mn ~ 5-30

Rheology-Processing/Ch.1 37

Sometimes, the dilute solution viscosity η of the polymer is usedto characterize molecular weights

η=solution viscosity K, a=empirical constants available in booksηo=solvent viscosity Mv=viscosity-average molecular weightC=concentration

av

ο

ο

cKM

Cη

ηη

0lim

Rheology-Processing/Ch.1 38

TYPICAL MWD

Rheology-Processing/Ch.1 39

POLYMER PROPERTIES

Like in metals (e.g. steel) we can measure tensile properties i.e. stress(σ) vs strain (ε), σ=Εε, where E the Young’s modulus (or tensilemodulus) (N/m2=Pa)

Slope in a stress-strain diagram → E

Rheology-Processing/Ch.1 40

Typical values of tensile modulus are usually in GPa (=106 Pa)

LDPE 0.2 GPa

HDPE 1.0 GPa

NYLON-66 2.0 GPa

PVC 2.5 GPa

PS 3.4 GPa

STEEL 210 GPa

Rheology-Processing/Ch.1 41

The “strength” of steel comes from primary chemical bonds The “weakness” of plastics comes from the weak cohesive forces (Van der

Waals) between the entangled and coiled long chains

So, to produce SUPER STRONG plastics we must align the chains → thecarbon-carbon bonds will give us a lot of strength!!!e.g. Single PE filaments have been produced with E=260 GPa (steel=210 GPa)

Can be achieved by special processing techniques e.g. extrusion and drawingof fibers at low temperatures.

Rheology-Processing/Ch.1 42

Tensile modulus E depends on temperature

It is all a question aboutchain mobility (none forglass, a lot for melt)

Crystallinity inhibits chainmobility and gives hardnessto polymer.

glass transition

region

logE

Temperature

glass

TgTm

amorphous

polymers

semi-crystalline

polymers

rubberymelt

Rheology-Processing/Ch.1 43

TIME-DEPENDENCE

One important characteristic ofSOLID polymers is the timedependence of their properties. e.g.Rigid PVC may have a high modulusat high extension rates while it haslower modulus at low extensionrates

Rheology-Processing/Ch.1 44

While simple tensile test is adequate for design purposes with steel, plasticsmust be subjected to additional testing especially for their long-timeproperties. Under constant stress, polymers tend to “creep” i.e. strainincreases with time

Rheology-Processing/Ch.1 45

Break

SLOPE=E (modulus)

stre

ss

strain

TENSILE MODULUS VS TENSILE STRENGTH

The TENSILE MODULUS is determined fromthe tangent at the origin in the stress-straindiagram

TENSILE STRENGTH is the ratio of the forceapplied to the material at rupture to itsoriginal cross-section area (σB=F/A). Thisproperty is typically called ultimate tensilestrength, i.e. the strength at break.

For commodity plastics: E=O(1 GPa)σΒ=Ο(20 MPa)

σB

Rheology-Processing/Ch.1 46

Diagrams of TENSILE STRENGTHversus TENSILE MODULUS areavailable (mainly used forclassification purposes).

For design with plastics we needthe tensile modulus and strength,flexural modulus, compressivestrength, impact strength andtime dependent properties likecreep.

Rheology-Processing/Ch.1 47

POLYMER PROCESSING

METHODS

Rheology-Processing/Ch.1 48

SINGLE SCREW EXTRUSION

Rheology-Processing/Ch.1 49

TWIN SCREW EXTRUSION

Rheology-Processing/Ch.1 50

blown film extrusion

Rheology-Processing/Ch.1 51

INJECTION MOLDING

Rheology-Processing/Ch.1 52

CALENDERING

Velcro

Rheology-Processing/Ch.1 53

COMPRESSION MOLDING

Rheology-Processing/Ch.1 54

BLOW MOLDING

Rheology-Processing/Ch.1 55

THERMOFORMING

Rheology-Processing/Ch.1 56

ADDITIVE MANUFACTURING

Selective Laser Sintering (SLS)

Rheology-Processing/Ch.1 57

ADDITIVE MANUFACTURING

Fused Deposition Modeling (FDM)

Rheology-Processing/Ch.1 58

In all of the previous processes the polymer is a MELT(in high temperature) which means that it FLOWS likea LIQUID inside the many channels of the processingequipment (e.g. inside the extruder and the extrusiondie).

Understanding the FLUID MECHANICS is essential!!